With the Transportation Security Administration (TSA) ramping up its use of full-body scanners in airports just at the busiest travel time of the year, passengers are extra cautious about what health risks, if any, are posed by the new scanners.
But the consensus among radiation experts and medical physicists is that the scanners used in airports produce such minuscule levels of radiation that they pose no real health risks.
However, others pose questions about the machines -- what effects will the low-dose X-rays have on skin and what would happen if a machine's off mechanism jammed and delivered a dose of radiation that is millions of times higher than intended?
Airports use two types of scanning technology -- millimeter wave scanners, which use radio waves and do not expose people to X-rays, and backscatter scanners, which use very low levels of X-rays.
It's the backscatter scanners -- which create an anatomically accurate image that reveals if anything is hidden under a person's clothing -- that have been the subject of controversy in the past week.
The full-body backscatter scanners are now deployed in 70 of the 450 airports in the U.S., according to the TSA. Physical pat-downs are performed on people who refuse the full-body scan.
With amped-up media scrutiny on the full-body scans, and with many patients preparing for holiday travel, an increasing number of physicians have been calling Kelly Classic, a health physicist at the Mayo Clinic and asking her what they should tell their patients.
Classic's department even issued a statement that Mayo doctors can refer to when explaining to patients if the full-body scanners emit enough harmful radiation to pose a health risk.
The message: "The amount of radiation is almost insignificant."
Classic tells Mayo doctors to give their patients the following comparisons:
The amount of radiation from one full-body airport scan is equivalent to two minutes of flying in an airplane, to sleeping next to another person for the night, and to 40 minutes of just living.
"There are so many common things we're exposed to that produce radiation," she told MedPage Today. "This [an airport scan] is a pretty minor piece of that."
The U.S. Department of Homeland Security echoes the assessment that the radiation from one full-body scan is equivalent to the radiation a person is exposed to from two minutes of flying at cruising altitude.
Put another way, a traveler would require more than 1,000 such scans in a year to reach the effective dose equal to one standard chest X-ray, the American College of Radiology (ACR) said in a statement posted to the group's website.
"The ACR is not aware of any evidence that either of the scanning technologies that the TSA is considering would present significant biological effects for passengers screened," the ACR said.
A group of scientists from the University of California San Francisco (UCSF) first brought the issue to the forefront of the radiology community more than seven months ago.
John Sedat, PhD, professor emeritus in UCSF's department of biochemistry and biophysics, and several colleagues wrote a letter to the White House in April expressing their concern over the "potential serious health risks" of the full-body backscatter scans.
The scientists said the device has not been adequately tested and laid out a number of issues that they say are unknown, including the effects of radiation on older passengers, pregnant passengers, and passengers with HIV or cancer, and what effect the low doses of radiation might have on breast tissue directly beneath the skin, on corneas, and on testicles.
However, since that letter, scientists at Johns Hopkins' applied physics lab tested the most commonly used machine -- the Rapiscan -- for the Department of Homeland Security and TSA.
Their August report found the doses of radiation delivered to a person standing in the scanner are well below those laid out by the American National Standards Institute (ANSI). Even if a person had 46 screenings a day every single day for a year, the dosage would still be just one-quarter of the total amount of radiation that the ANSI recommends not be exceeded in a given year, according to the report.
However, the scientists pointed out that there are areas well above the unit, and at the entry and exit points where the radiation dose could exceed the per year dosage cap laid out by ANSI.
But Peter Rez, PhD, professor of physics at Arizona State University questioned the radiation figures from the John Hopkins scientists. By his own mathematical calculations, the doses emitted from the backscatter machines are much higher, although still not high enough to pose a serious health risk.
The real risk posed by the machines is if they jammed and failed to turn off, which could result in blasting a person with enough radiation to cause serious burns, Rez told MedPage Today.
"Mechanical things break down and if that beam were to stop at one point, you'd get a very high dose on that one part," Rez said. "That's what worries me the most."
The machines do have fail-safe methods built in, but Rez said he won't trust them until he sees engineering studies proving the fail-safes are reliable.
"It's one thing to have an X-ray in a lab at a hospital that is looked over by trained people, but it's quite another to have it in an airport terminal with all the hustle and bustle and the TSA people looking over it."
Rez recently opted out of the full-body scan before boarding a flight from Florida to Arizona, which meant he was subjected instead to what he called the "big grope."
But the chief physicist at John Hopkins -- who was not involved in writing the report for DHS and TSA -- told MedPage Today that even if the machines failed to turn off, a person would have to stand in the scanner for hours before being exposed to radiation doses high enough to cause burns.
"In case the machine gets stuck, the radiation output is not that high," said Mahadevappa Mahesh, MS, PhD, who is also an associate professor of radiology and cardiology.
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